The invention relates to machine alignment, and more particularly, to a noise resistant laser system for aligning machines. The invention is also intended to be used for routine machine inspection in manufacturing.
Many industrial processes mandate that accurate spatial relationships be maintained between machine elements. Accurate machine alignment is essential for maintaining quality in manufacturing. Improperly machined parts increase manufacturing costs and adversely affect customer goodwill. Misalignment of machine elements can also result in broken tools and lost production.
Until recently, equipment for machine alignment consisted primarily of dial indicators, levels, feeler gauges, stretched piano wires, telescopes and the like. This type of equipment is still used by some manufacturers.
Some manufacturing requires levels of precision that cannot be readily obtained with mechanical, electromechanical and optical alignment equipment. For example, highly automated manufacturing requires very precise spatial and angular orientation of tools relative to one another and relative to workpieces. Improper alignment in multiple station machines results in high reject rates and tool breakage. Even a short down time for a highly automated transfer line can be extremely expensive.
The need for increased precision and for minimizing machine down time has made laser alignment systems a desirable alternative in many companies. Alignment systems employing lasers and photodetector targets were introduced about thirty years ago. A typical laser alignment system consists of a laser emitter, at least one photodetector target that produces electrical output signals capable of identifying the locations at which the target is impinged, and an output device for processing the target output signals and displaying the results.
In a typical application, a laser emitter and a photodetector target are attached to a machine with special adapters at predetermined locations and machine components are adjusted to align the machine.
By way of example, Duey et al. U.S. Pat. No. 5,148,232 issued on Sep. 15, 1992, discloses an apparatus and method for aligning a crankpin grinding machine. The apparatus consists of a laser emitter for projecting a narrow collimated beam of light, a photodetector target which produces an output which is indicative of the position of the laser beam on the target, special adapters to mount the laser and target on the crankpin grinding machine, and an input/output unit to process the output of the target and display information to an operator.
The alignment system reduces time and cost for aligning a crankpin grinding machine and provides the opportunity of performing regularly scheduled maintenance during machine idle time rather than "as needed".
One problem with existing laser machine alignment systems is that their performance is affected by ambient light. This problem exists because laser machine alignment systems utilize low power semiconductor lasers because of space limitations and worker safety. The low power lasers result in low signal to noise ratios which cause fluctuations in display unit readouts. The fluctuations in the readouts are annoying and limit the degree of accuracy of readings on the display units.
In some laser systems, targets have optical filters for blocking out light waves of higher frequencies than the laser frequency. By way of example, in the QUADRA-BEAM.TM. infrared laser alignment system, manufactured by the Intra Corporation of Westland, Mich., an optical filter with a cutoff wave length above the infrared region is used to block out visible light from sources such as industrial sodium vapor, mercury vapor and fluorescent lights.
Although the QUADRA-BEAM.TM. filter provides some improvement, it is not totally effective in reducing ambient light noise. The frequency of this noise has been determined to be harmonically related to the natural frequency of a power line which varies from country to country.
One possible solution to the ambient light noise problem is to increase the signal to noise ratio by increasing laser power. However, this is not desirable because it would expose workers to higher levels of radiation and increase the probability of eye and nervous system injuries.